Copper, the good, the bad, the ugly Dr Eric Wilkes
Why do we use copper at all? Copper has a long history of use in beverage production to remove unpleasant sulfur related smells. Analysis of 80,000 international wine show entries show ~0.9% of wines rejected for reduction, with no significant difference between closures.
What are these smells H 2 S 1.1-1.6µg/L rotten egg, sewage like DMS 25µg/L Blackcurrant, cooked cabbage, asparagus, canned corn MeSAc 40µg/L MeSH 1.8-3.1µg/L rotten cabbage, burnt rubber, putrification DMDS 10µg/L Vegetal, cabbage, intense onion like Sulfurous, cheesy, egg
The 1950s story. H 2 S H 2 S + Cu 2+ CuS Mercaptans CH 3 CH 2 SH + Cu 2+ Cu(CH 3 CH 2 S) 2 oxidation reduction DMDS CH 3 S-SCH 3 + Cu 2+ unreactive DMS CH 3 SCH 3 + Cu 2+ unreactive
But why doesn t it always work? Why don t the bench trials always reflect what I see in tank? Why does my wine go stinky again after it is treated in tank?
Myth 1, the size of copper additions. All the copper I add drops out as insoluble sulfide! Sulfide Copper Sulfate 1-2 μg/l 0.000002 g/l 0.5ppm 0.0005 g/l It is not unusual to see copper values increase at exactly the same rate as addition.
Myth 2, filtration does not really work. Clark, A. C., et al. (2015). "Copper(II) addition to white wines containing hydrogen sulfide: residual copper concentration and activity." Australian Journal of Grape and Wine Research 21(1): 30-39.
So what is this residual copper? Non-Labile Cu (µg/l) 900.0 800.0 700.0 600.0 500.0 400.0 300.0 200.0 100.0 Total Cu vs Non-labile Cu y = 0.943x - 9.6029 R² = 0.9758 0.0 0.00 100.00 200.00 300.00 400.00 500.00 600.00 700.00 800.00 900.00 Total Cu (µg/l) The majority of copper found in commercial wines is in a tightly bound non-labile form. A study of 52 commercial wines by Nikolaos Kontoudakis and Andrew Clark, Charles Sturt University. Clark, A.C. et al., 2016. Measurement of labile copper in wine by medium exchange stripping potentiometry utilising screen printed carbon electrodes. Talanta, 154(C), pp.431 437.
It is the form of copper that is important! Free H 2 S (µg/l) Free H 2 S vs Labile Cu (electrochemistry) 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 0.0 50.0 100.0 150.0 200.0 250.0 Electrochemically labile Cu (µg/l) Levels of electrochemically labile copper above 25 µg/l do limit the formation of free H 2 S But most of the copper is in non labile form which does not inhibit the presence of free H 2 S
Metals play a crucial role in wine chemistry!
Myth 3, the problem with fining trials High Oxygen Low Oxygen
So What?
Increased loss of positive thiols 3-MH (3-Mercaptohexan-1-ol) 3-MH [nmol/l] 90.0 85.0 80.0 75.0 70.0 65.0 60.0 55.0 control Cu Dr. Mandy Herbst-Johnstone School of Chemical Sciences The University of Auckland 50.0 0 14 28 time [days]
More rapid loss of SO 2 SO 2 cannot interact with O 2 directly. It requires the presence of metals such as copper and iron. FSO 2 (mg/l) 19 18 17 16 15 14 Sulfur Dioxide (free) 0 0.2 0.5 0.75 1.5 Copper (mg/l) After just six months in bottle! Danilewicz, J. (2007). Interaction of sulfur dioxide, polyphenols, and oxygen in a wine-model system: Central role of iron and copper. Am. J. Enol. Vitic vol. 58 no. 1 53-60
Increases in sulfides 3 H 2 S Clare Valley Riesling after 8 months. Relative Amounts of Cu vs H 2 S 2.5 70 2 1.5 1 0.5 0 Cu 0 mg/l Cu 0.2 mg/l Cu 0.5 mg/l Cu 0.75 mg/l Cu 1.5 mg/l H 2 S Concentration ppb 60 50 40 30 20 10 After just 2 months this chardonnay was already showing the impact of increased copper. 0 0 0.04 0.16 0.53 Cu Concentration ppm Remember, the threshold for H 2 S is about 1 for most people!
What are some of the triggers?
Time in bottle Shiraz - H 2 S Shiraz - MeSH Concentration (µg/l) 5 4 3 2 1 Control Cu Odour Threshold 1.1-1.6 µg/l Concentration (µg/l) 10 9 8 7 6 5 4 3 2 1 Control Cu Odour Threshold 1.8-3.1 µg/l 0 Day 1 Month 1 Month 3 Month 6 Month 12 0 Day 1 Month 1 Month 3 Month 6 Month 12 oxygen depletion oxygen depletion
Impact of copper timing H 2 S (µg/l) 14 12 10 8 6 4 In this trial from 2014 we looked at the impact on a wine of adding copper immediately after fermentation and just before bottling. The late copper addition led to significantly higher H 2 S. 2 0 Bottling Month 2 Month 8 Month 12 Early Cu + late Cu Early Cu But more importantly the impact was not apparent until 12 months after bottling.
SO 2, not necessarily benign 20 H 2 S - Shiraz 18 16 14 Increased H 2 S correlates with the addition of Cu and SO 2. µg/l 12 10 8 6 Day 1 Month 1 These trial were done under the exclusion oxygen. 4 2 0 H2S odour threshold 1.1-1.8µg/L Control Cu SO2 1 mg/l 60 mg/l Total SO 2 Cu + SO2
The impact of ph and copper As can be seen with this wine ph alone has little impact on the level of H 2 S generated. Chardonnay with 0.5 mg/l copper added In the presence of copper however ph has a major role in determining the levels of H 2 S generated. Bekker, M. Z., et al. (2016). "The effects of ph and copper on the formation of volatile sulfur compounds in Chardonnay and Shiraz wines post-bottling." Food Chemistry: 1-33. FOOD CHEMISTRY, Accepted manuscript. doi:10.1016/j.foodchem.2016.03.060
It is not just the copper! Relationship between Cu/Fe and H 2 S 3.00 R² = 0.9204 H 2 S 2.50 2.00 1.50 Cu/Fe ratio critical to H 2 S levels. Mn, Zn and Al also seen to have an impact on VSC s 1 1.00 0.50 At really high copper levels other stuff happens 0.00 0.0 1.0 2.0 3.0 4.0 5.0 6.0 Cu/Fe 1 Viviers, M.Z., Smith, M.E. & Wilkes, E.N., 2013. Effects of five metals on the evolution of hydrogen sulfide, methanethiol, and dimethyl sulfide during anaerobic storage of Chardonnay and Shiraz wines. Journal of Agricultural and, 61(50), pp.12385 12396.
Can t we manage this with a closure? MeSH 12.00 10.00 8.00 6.00 MeSH with time For at least the first 2 years the differences are no greater than impact of metals in other trials O T R Average results for 9 different closures. Final level does not correlate with closure OTR! 4.00 2.00 0.00 0 5 10 15 20 25 30 35 40 Months in Bottle Pattern typical of what we see as the available O 2 / SO 2 environment changes.
Do we have any alternatives? 2014 Metal Chelation Trial H 2 S (µg/l) 14 12 10 8 6 4 2 0 Day 0 Month 5 Month 9 Month 12 Timepoints Control Tannin Using a commercial tannin marketed for its ability to add freshness we see a significant difference in H 2 S post 9 months in bottle. 2015 Metal Chelation Trial Using a cross linked polymer to reduce Cu and Fe we see a reduction of H 2 S after 9 months in bottle. Have we removed VSC s with the Cu? H 2 S (µg/l) 12 10 8 6 4 2 Control Divergan 0 Day 0 Month 2 Month 4 Month 12 Timepoints
So what can we do? Best time to add is at the near the end of fermentation Eliminate the potential precursors as early as possible Use the active yeast to remove as much of the excess copper as possible If you have add it later Know what sulfur compounds you are treating (copper/cadmium test) Look at using copper in bound forms (copper citrate/bentonite) Use active yeast to strip the residual copper. When available try using cross linked polymers to remove the copper (and possibly the bound sulfides). Never add on the day of bottling.
Acknowledgements Paul Smith Sabrina Reshcke Marlize Bekker Mark Smith Martin Day Mandy Herbst-Johnstone (Uni of Auckland) Andrew Clark (CSU) Nikolaos Kontoudakis (CSU) Treasury Wine Estates The rest of the AWRI team. This work is supported by Australia s grapegrowers and winemakers through their investment body Wine Australia, with matching funds from the Australian Government. The AWRI is a member of the Wine Innovation Cluster in Adelaide.
Thankyou Questions?